Advantages sof direct sampling are that areas hardest to clean and which are reasonably accessible can be evaluated, leading to establishing a level of contamination or residue per given surface area.

直接取样的好处是可以评估难以清洗和相当容易接近的区域，使得可确定每个给出的表面区域的污染物或残留物的级别。

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The standard states that the citric acid-sodium nitrate treatment is the least hazardous for removal of free iron and other metallic contamination and light surface contamination.

该标准声明：柠檬酸-硝酸钠处理在去除游离铁合其他金属污染和轻的表面污染物时，危险性最低。

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The presence of exogenous surface contamination, including dirt, grease, free iron from contact with steel tooling, and so forth, may interfere with the formation of the passive film.

外生的表面污染，包括：尘土、油脂、来自钢铁加工的游离铁等等，可以影响到钝化膜的生成。

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And what prevents soil and surface water contamination from countless units that ultimately wind up in landfills?

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In Washtenaw County and Ann Arbor, Michigan a 1, 4-Dioxane, in groundwater and surface soil contamination from Gelman Science, persists after nearly 20 years of cleanup activities and has now spread in groundwater to an area over three miles long and a mile wide.

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The remaining soil contamination is located several feet below uncontaminated surface soil.

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